1. Field of the Invention
This invention is in the field of heat treatment of finely divided materials of the type used for the manufacture of cement which involves the combination of pre-heating, calcining, sintering, and cooling and is specifically directed to improving the sintering operation by carrying it out in a suspension type reaction zone.
2. Description of the Prior Art
In the dry process of manufacturing cement, the cement raw material which ranges in particle size from fine-grained materials to powder is delivered to a material pre-heater through which it passes in counter-current and/or parallel flow to hot treatment gases which are generated in a rotary kiln in which the material is sintered at high temperatures. A cement clinker is formed by sintering in the kiln, and this clinker is cooled in a cooler connected to the rotary kiln for further processing. The material pre-heater represents a stationary system part which is not very susceptible to wear, but the rotary kiln has a series of moving rotary parts which are subject to high wear in the dusty and high temperature atmosphere. The connections of the rotary kiln to the stationary material pre-heater or to the stationary material cooler are particularly in need of intensive maintenance and monitoring.
Some attempts have been made to replace the rotary kiln as a calcining or sintering apparatus through the use of a pipe-shaped horizontally disposed chamber, as suggested in German AS No. 1,807,292. Pre-heated fine material, hot cooler exhaust gases, and gaseous fuel are blown into the chamber from an end face. Cold cooling air is blown in by means of a closed circular pipe line at the end of the horizontal, pipe-shaped combustion chamber. In the heat treatment of cement raw material, this combustion chamber is not particularly advantageous. For example, the combustion chamber can only be charged with gaseous fuels. In order to achieve uniform distribution of the material in the combustion chamber, high flow rates must be employed. In this way, the material is subjected to treatment times which are too short so that the sintering of the material is not always carried to completion. In order to avoid formation of incrustations in the combustion chamber, the cooling air must be blown into the combustion chamber from the end. The thermal efficiency of the entire system is correspondingly low. These disadvantages also apply to a stationary combustion device in which a cold twisting stream is maintained in order to avoid material incrustations in the combustion chamber as suggested by German OS No. 2,350,768.
Finally, a system for the heat treatment of fine-grained material in a combustion chamber utilizing solid or liquid fuels is described in German OS No. 2,629,082. These fuels, however, must first be gasified in a separate gasification device because the fuel must be gaseous when it is introduced into the combustion chamber. This very significantly increases the cost of the system, since appropriate control and process engineering devices are required. The system of this publication is also pretty much confined to fine-grained hydrated aluminas or other fine-grained ores.